Phyllosilicate minerals such as clay are important industrial materials. As an example, bentonite is one type of clay composed of montmorillonite. Montmorillonite is a clay mineral comprised of stacks of SiO4 tetrahedra sandwiched between two sheets of octahedrally coordinated aluminum, magnesium or iron. Substitution of lower valence ions for some of the higher valence ones in the octahedral sheets creates a negative charge imbalance that traps cations, most often sodium (Na+) or calcium (Ca2+), between the stacked sandwiches. The absorption power of various types of bentonite clay is determined by which cation is present and in what amount. Because sodium ions have a larger hydration sphere than calcium ions do, sodium bentonite can absorb more moisture than its calcium counterpart.
Bentonite clay has a number of different uses, for example, it can be used in drilling mud, or used as a binder, absorbent, decolorizing agent, clarifier, or it can be subjected to still other uses. Bentonite clay can be used to produce absorbent products, for example for absorbing chemicals, oil or grease, or for absorbing animal waste, such as in litter for domestic animals such as cats. Cat litter is an important commercial product, and requires a material that can absorb moisture and, preferably, trap odors. Traditional litter materials such as ashes, dirt and sand, and even clays traditionally used as kitty litter that do not clump significantly in the presence of moisture, must be discarded and replaced fairly often. Bentonite clay tends to clump in the presence of moisture, facilitating the removal of soiled litter by removing the clumps of wet bentonite clay created by urine, leaving behind clean litter. Bentonite clay can also sequester urine and trap ammonia (NH4+) produced from urine degradation, to help control odors.
In order to be manufactured into absorbent products, phyllosilicate minerals, including clay and including bentonite clay, must generally first be dried. Traditionally, bentonite clay has been dried using conventional thermal systems where heat energy is applied to the outside of the clay particles, warming the clay to a temperature required to evaporate water and dry the clay. This conventional process is inefficient for a number of reasons, including because the clay has excellent insulative properties due to its structure. The clay thus resists the absorption of heat from the outside of the clay particle to the inside of the clay particle.
The drying of phyllosilicate minerals, including clay, can be complicated by the fact that phyllosilicate minerals have properties of agglomeration, which can make such materials more difficult to dry than other bulk materials such as aggregates. There is a need for improved methods and apparatus for drying phyllosilicate minerals, including clay, including bentonite clay.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.